My invention comprises improvements in a hydrokinetic torque converter transmission of the kind shown in U.S. Pat. No. 4,509,389. That patent describes a planetary transaxle having two simple planetary gear sets, a final drive and a differential assembly on one axis and a converter and converter lock-up clutch arranged on a spaced, parallel axis, the latter corresponding to the axis of the crankshaft of an internal combustion engine. A drive chain and sprocket assembly transfers torque from the turbine of the torque converter to torque input elements of the gearing.
The lock-up clutch for the torque converter of U.S. Pat. No. 4,509,389 includes a damper assembly that is intended to cushion and to dampen torsional vibrations resulting from engine torque fluctuations, and from inertia torque disturbances transmitted through the clutch. The lock-up clutch of the '389 patent includes a piston plate having a friction surface situated at a radially outward location and a friction surface on the adjacent wall of the impeller housing for the torque converter.
The clutch piston and the adjacent wall of the impeller housing define a control pressure chamber. Control pressure in the control pressure chamber establishes a clutch release force on the clutch piston. Control pressure is supplied to the pressure chamber through porting in sleeve shafts extending through the converter. The fluid supplied to that chamber flows across the friction surfaces of the lock-up clutch piston. Radial flow through the pressure chamber and across the friction surfaces establishes a control force that tends to release the clutch. That flow is added to the torus circuit supply fluid which is distributed through the torus circuit through other annular passages in the sleeve shaft arrangement for the converter. The torus flow through the converter exits through an exhaust flow path which communicates with a transmission oil cooler.
An early prior art teaching of a clutch of this kind is shown in General et al., U.S. Pat. No. 3,252,352. That patent also describes a clutch plate which is actuated by circuit pressure within the torus circuit of a converter. The clutch is released as pressure is admitted to the annular space defined by the piston and the adjacent impeller wall. Later examples of converters with lock-up clutches of this kind may be seen in U.S. Pat. Nos. 4,271,939, 3,977,502 and 3,730,315.
The '502 patent and the '315 patent show lock-up clutches that are designed to accommodate a continuous slip so that a portion of the torque transferred from the engine through the converter is distributed mechanically through the slipping clutch and the balance of the torque is distributed hydrokinetically through the torque converter. In each instance, the torque output element of the clutch is connected to the turbine shaft so the mechanical portion of the torque flow path is additive with respect to the hydrokinetic torque flow path.